The invention relates to digital tape drive storage devices, and in particular, to an improved roller guiding method for delivery of magnetic tape media along a tape path between a tape drive employing a single reel and a tape cartridge employing a single reel.
Digital data is stored on tape drives utilizing a variety of designs, but in all cases, magnetic tape media is wound between a pair of tape reels as data is transferred to or from the tape media. In the art of data storage, the physical space required to store data is an important concern. To conserve space, tape drives often use a single reel tape cartridge design. The single reel design utilizes a supply reel located within the tape cartridge and a takeup reel located within the tape drive. After the tape cartridge is inserted into the tape drive, the tape media is connected to the takeup reel and wound along a tape path internal to the tape drive.
One example of a tape path is a guide roller tape path located between the supply reel and the takeup reel. The guide roller tape path uses a plurality of guide rollers to guide the tape media as it is wound between the supply reel and the takeup reel. Guide roller tape paths have the advantage of reducing friction in the tape path to that of rolling friction caused by components such as ball bearings.
A tape transducer, or tape head as it is commonly referred to in the art, located in the tape path, reads and writes digital data as the tape media passes over the tape head. The digital data is written and read from the tape media in tracks running in a longitudinal direction relative to the tape media. To read or write data on a specific track, the tape head must align with that track as the tape media passes over the tape head. To prevent errors in reading and writing data, the tape path traveled by the tape media must be reproducible with a high degree of accuracy. For purposes of this application tracking is defined as the alignment of the tape head with an individual tape track on the tape media.
Improvements in the art of tape heads have increased the number of tracks that can be included on magnetic tape media. As a result, individual tracks are narrower and require higher tolerances of tape path reproducibility to maintain alignment of a desired track with the tape head. Alignment of a specific tape track with the tape head is especially critical during data writing because a misalignment can result in writing over data contained on adjacent tracks.
It is a problem in tape drives employing a guide roller tape path to achieve these high tolerances in tape path reproducibility in light of the narrower tracks on the tape media. The quality of reading and writing data is functionally related to the tape media to tape head contact and the alignment of the desired tape track with the tape head. The alignment of a desired tape track with the tape head and the tape media to tape head contact is affected by several factors during tape drive operation. One factor is tape tension during winding of the tape media through the tape path. Inconsistencies in tape tension move the tape media slightly up or down as it passes over the guide rollers. This movement causes the stationary tape head to lose tracking of a particular tape track.
Another factor is inconsistencies in tape cut. Industry standards permit a positive or negative variation in tape media width of approximately 0.0004 inches over the length of the tape media. These variations also cause the tape media to move slightly up or down the guide rollers causing the tape head to lose tracking. Yet another factor is tape stretch due to wear. Over the course of tape media life, friction in the tape path causes tape degradation that affects how the tape media travels through the tape path.
For these reasons, a need exists in the art for an improved roller guiding system that provides improved tracking of tape media as it is wound through the tape path.
The present invention overcomes the problems outlined above and advances the art by providing an improved roller guiding method for delivery of tape media along a tape path. A first advantage of the present roller guiding method is the formation of a dynamic tape path that continually realigns the desired tape track with the tape head during tape drive operation. A second advantage of the present roller guiding method is improved tracking and tension control. A third advantage of the present roller guiding method is a substantial increase in the number of tape tracks accommodated by a tape drive employing the roller guiding method. A fourth advantage of the present roller guiding system is a reduction in errors during tape drive operation.
The roller guiding system comprises a plurality of guide rollers configured to continually adjust the tape media path of travel during tape drive operation to maintain alignment of the tape head with a particular tape track. In a first embodiment of the roller guiding system, four guide rollers are used to guide the tape media along the tape path between the takeup reel in the tape drive and the supply reel in the tape cartridge. A first pair of guide rollers are identical in design and operation and include a central crown on their tape media contact surfaces. A second pair of guide rollers are identical in their design and operation and include a tapered tape media contact surface that travels from a widest point at the top of the guide roller to a narrowest point at the bottom of the guide roller. All four guide rollers include a tape media contact surface that is slightly wider than the tape media to allow the tape media to pass unobstructed over the tape media contact surface of each guide roller.
The second pair of guide rollers are connected to the tape drive deck between the first pair of guide rollers. The tape head is located between the second pair of guide rollers. During operation of the tape drive, the tapered contact surface of the second pair of guide rollers applies an upward force on the tape media causing it to maintain constant alignment with the top edge of the second pair of guide rollers. As the tape media varies during winding the upward force holds the tape media against the top edge of the guide rollers, which in turn realigns the tape track with the tape head.
In a second embodiment of the roller guiding system, the tapered contact surface of the second pair of guide rollers is inverted and travels from a widest point at the bottom of the guide roller to a narrowest point at the top of the guide roller. In preferred embodiments at least one of the guide rollers includes spiral grooves circumscribing its tape media contact surface.